Page Layout
Once the information to be displayed is classified, the data must be displayed. This is the process of page layout, which can be broken into: layout within parts and layout within the whole. Layout within parts of a display involves the selected use of visual variables to highlight a part or parts of a data set or display. This is the establishment of graphic hierarchies and involves two techniques: visual isolation, and visual levels (MacEachren 1992, 27) (see Figures 1.1 and 1.7.
Figure 2.8 Visual isolation. The letters in each word `go together,' as do the lines and their labels, but not the lines and the display title.
Visual isolation is the use of visual variables to give the appearance of the separateness of part of a display. The visual variables that can accomplish this include location, size, focus, value, hue, saturation, texture and orientation. Location is the most obvious control--display items that are not close together will not generally be associated (see Figure 2.8). Size can influence isolation because any feature that is drawn smaller than the area allocated to it, will appear separate from the surroundings (this is done in cartograms). Focus influences isolation because unfocused, fuzzy symbols blend into the surrounding, reducing isolation. Value, hue, saturation, texture and orientation influence isolation by enabling one item to be displayed in a manner that is noticeably different than its surroundings (dark blue surround by yellow, for example) and thus isolating it.
Figure 2.9 Visual levels. Darker value usually is a foreground (at a higher level) than lighter values, particularly on white backgrounds.
Like visual isolation, visual levels are used to separate an item from its surroundings, but whereas visual isolation seeks to accomplish that in the x-y space of the page, visual levels give the appearance of separation in the third dimension. The visual variable that control visual levels are: size, value, saturation, texture, focus and hue. These visual variables all play a part in depth perception. Size controls visual levels because things that appear larger, appear to be closer. Value controls visual levels by control of contrast from the display background--objects with high contrast will appear above the background (see Figure 2.9). Saturation controls contrast because intense colors appear to be closer than less-intense colors. Texture influences visual levels because coarse textures appear to be closer to the observer. Focus influences visual levels because sharply focused objects appear to be closer than fuzzy objects. Hue influences visual levels because, at a constant value and saturation, yellow is more noticeable than other colors, but the influence of hue can be hard to predict and control.
In designing a page, the layout within the whole page involves the use of space (and for animation, time) to present different parts of a message. The type of display has an influence on what can, and should, be said on an image. Paper displays can be of any size, but two are of more importance: 8.5 by 11 inch paper, and full size electrostatic plotters. 8.5 by 11 inch paper is probably the most common format for graphic publication. Its small size restricts the amount of information than can be shown on one page, but generally high resolution and the ability of the reader to study the graphic at length permit a great deal of information communication. The portrait orientation, which is normally used with text, limits the left-right extent of a display, so graphics that have a large left-right extent should be displayed as landscape, when the graphic cannot be redesigned to take advantage of the more common reading orientation. Generally the primary part of the display should be shown with a maximum left-right extent. Titles can then be placed above, and additional information such as legends and locator diagrams can be placed below the primary part of the display.
Large size paper products, such as posters, can be created with less emphasis on the orientation of the page, and more emphasis on the size and shape of the area of interest. Orientation of the page should follow the larger axis of the data set. Additional information should then be placed around the main part of the graphic, in order to take advantage of `dead space.'
Figure
2.10 The apparent size of 16 point text
from 8 feet away (top) is the same as 6 point
lettering from 1.5 feet (bottom) (MacEachren 1992, 71).
Slides and overheads limit the amount of data that can be displayed because of the distance that they force on the viewer (see Figure 2.10). The farther a viewer is from the display, the smaller the display will appear, limiting the visibility of detail. This implies that the page layout decisions for slides and overheads require greater generalization in both space and data. Only the most important information needed to support a point should be included on the display. As such, additional information such as legends and locator diagrams should not be included. This allows the maximization of the available space for data display, and like posters, the orientation of the display should be aligned with the larger axis of the data area. This loss of data on the graphic is offset by the explanations of the presentor of the slide, overhead or video.
Video involves both high resolution computer monitors, and lower resolution National Television Standards Committee displays. Video displays must, like slides, take into account the distance from the viewer, as well as lower resolutions and display flicker. Minimize the amount of ancillary information, in order to maximize the amount of space available for the primary data. Like slides, this loss of visual information must be offset by audio explanations.
Titles and Type
The text that is used to label a map or graphic should be selected carefully. This involves the determination of what should be labeled, how it should be labeled, where the labeling should be placed, and what type of lettering to use. Which items must be labeled should be identified during the planning phases of the map design, particularly in identification of the communication goal--label those things that are necessary to accomplish the goal. Additional labeling may be necessary for locational reference, etc., but this ancillary labelling should be kept to a minimum in order to emphasize the new information.
As with the amount of features that get labelled, the amount of text in each label should be kept to a minimum. Often leading 'a,' 'an' and 'the's can be dropped from labels. Phrases such as 'the city of,' 'plot of' or 'Legend' can also be dropped without loss of information and result in an improvement in communication by getting rid of the clutter.
Labels should be placed on or near the object they label. Locations for titles can include prominent positions such as top center, but may also include making use of otherwise empty space (such as using the Gulf of Mexico's space in a map of Florida). Labels of point features should, when possible, be put at the upper left of the feature. Labels of linear features should be placed on straight sections of the feature, or if necessary fit along a smooth curve, and be oriented for maximum readability (top up, whenever possible). Area features should be labeled inside their boundaries, when possible. Although it is not entirely unavoidable, text should not be broken up by linear features or area boundaries; it may be preferable to have a break in the line, although this can be difficult to accomplish in ARC/INFO.
There are two general classes of fonts that are used for cartographic displays, roman and sans-serif, both of which can be italicized, underlined, etc. Roman fonts, such as the font used for this text, have 'serifs'--the small extension at the end of the strokes that make up the character. These fonts usually are more legible than fonts without (sans) serifs, particularly for small text. Sans-serif fonts are simpler, but are generally best used only for titles and other large text. For either type of font that may be used to label a body of water, it is cartographic tradition to use an italic font. This may connotate a sense of flowing.
The size of text influences legibility, particularly when the speed of a presentation is controlled by the presenter, rather than the reader. For paper displays that the reader will be able to study at length, text as small as 5 points (0.07 inches) can be used. Differences in text sizes should be at least 35% (0.07\5 pt, 0.095\7 pt, 0.13\9 pt, etc.) (Keats, 1982). For paper displays which are not available in depth study (such as flip charts and posters) the following suggestion for slides and overhead are more appropriate, although detail information could be included in posters.
For slides and overheads, not only must there be less text, but the text should be larger (see Figure 2.10). As a general rule text should be at least 18 point with larger differences than paper (50%) (MacEachren 1992, 71). Video displays also need to make use of large points sizes, because of lower resolution and with some systems, flicker.
Insets and Legends
There are two main types of insets: locator diagrams and additional graphics. Locator diagrams show the location of a smaller area, in relation to a larger and presumably more well known area (see Figure 2.11). When multiple graphics are generated for the same region, only one locator diagram should be needed, and it may be advisable simply to make the locator diagram a separate graphic. For displays which need integrated location diagrams, they should be visually isolated--the diagram should be secondary to the main display. Therefore avoid bright colors, if not colors entirely, but ensure the area of the main display is readily discernible.
Figure 2.11 A simple locator diagram.
Other graphics include legends, north arrows, scales and, for bi- or multivariate displays, monovariate maps. Legends must convey the information necessary to extract information from the main display. North arrows assist in orientation when north is not at the top, which it does not have to be. For maps to be presented to an international audience, include a north arrow, because south may be expected at the top (as is the Chinese custom). For maps where a large and hopefully well-known area is displayed (the United States or a subset of them, for example), a north arrow is not needed. Map scales, like north arrows, are not necessary for maps of well known areas and generally are not needed, unless the map may be used for measurement of extent. As suggested by Olson (1980), monovariate maps may be helpful in assisting readers who are not familiar with bi- or multivariate maps. These single variable maps should be designed to be both isolated and at a lower level in the visual hierarchy than the main display. Monochrome displays may be the most appropriate technique for all but nominal data.
Because of the requirements of different media, the amount of information that should be carried in a legend varies, as does the need for a legend. Because of the generalization that goes into slides and video displays, the need for legends should be minimal, particularly when the presenter is available to answer questions. A slide for a legend may be a waste, because it cannot be referred back to, and handing out a legend before a presentation may only serve to focus attention on the legend, not on the data that is being presented.
Paper displays, particularly those where the author is not available to answer questions, require the most thoughtful use of additional graphics. Explanations of data must be written out on the graphic. For bi- and multivariate displays, the mapping technique should be explained, and monovariate maps should be included. Legends should present the character of the data (data level, continuous or discontinuous, classification system used). This can, in part, be accomplished by defining discreet variable symbols separately with a label on each symbol, and by defining continuous variables as a continuum with breakpoints, rather than midpoints, labeled (see the legends in Figures 5.1 and 5.2, for example).
An approach to legend design that may be most helpful to inexperienced map readers is natural legends (see Figures 6.2 and 9.1). Natural legend design is particularly helpful with abstract symbolization, such as isolines, which can be difficult to interpret by a novice (especially when only given a contour interval). By providing a legend that shows isolines on a surface and spot values, the concept of a continuous surface and how data values are shown can be communicated. Isoline data, particularly when several data items are shown together, can be displayed as a single-variable, fishnet inset; this will convey the concept of a continuous surface and allow analysis of individual data sets, in addition to the presentation of the interplay of multiple data sets in the main display.